1. Field of the Invention
This invention relates to a process for presteaming or hydro-thermally treating a zeolite catalyst so as to substantially retain its initial activity and to a process for the preparation of superior zeolite catalysts to be used in high pressure methanol-to-gasoline (MTG) reactions.
2. Background of the Invention
Acid-catalyzed methanol-to-gasoline (MTG) reactions conducted at elevated temperatures and pressures result in the rapid degeneration of catalyst activity. It is well known in the art that mild-to-severely steamed zeolite catalysts provide improved stability but suffer from lowered activity in acid-catalyzed reactions.
Much of the prior art in this area deals with severely steamed zeolite catalysts in reactions such as xylene isomerization.
U.S. Pat. No. 4,224,141 (Morrison et al) discloses a xylene isomerization process with a catalyst steamed at a temperature in excess of 538.degree. C. (1000.degree. F.) for a period of time longer than 15 hours. The resulting catalyst is highly stable, but suffers from lowered activity.
U.S. Pat. No. 4,188,282 (Tabak et al) discloses a xylene isomerization process using a catalyst with a silica/alumina ratio of at least 200. The catalyst is severely steamed to a lowered activity as described in U.S. Pat. No. 4,016,218 (Haag et al) and U.S. Pat. No. 3,965,209 (Butter et al).
U.S. Pat. No. 4,236,996 (Tabak et al) discloses a xylene isomerization process wherein the catalyst is steamed at a high temperature to reduce the activity such that the conversion reaction temperature must be increased by at least 10.degree. C. to equal the conversion capability of an unsteamed zeolite.
U.S. Pat. No. 3,965,209 (Butter et al) discloses a process whereby the zeolite is steamed to reduce the alpha activity to less than 500 by treating the zeolite in a steam atmosphere at a temperature of from 250.degree. C. to about 1000.degree. C. (526.degree. F. to about 2026.degree. F.) for from about 1/2 hour to 100 hours.
U.S. Pat. No. 4,326,994 (Haag et al) discloses a process whereby a zeolite is steamed to activate or increase its alpha activity.
U.S. Pat. No. 3,969,426 (Owen et al) discloses a process for converting methanol to an aliphatic product and highly aromatic product boiling in the gasoline boiling range over a ZSM-5 crystalline zeolite.
U.S. Pat. No. 4,326,994 (Haag et al) discloses acid zeolite catalysts of increased activity which are prepared by contacting the acid catalysts with water for a sufficient time, temperature, and water partial pressure to bring about the enhanced activity. The contact water can be produced in situ as, for example, in alcohol dehydration to produce olefins and steam (column 7, line 56).
The present invention differs from the U.S. Pat. No. 4,326,994 patent with respect to the reaction conditions which the methanol feed undergoes. The U.S. Pat. No. 4,326,994 discloses conditions of moderate temperature, pressure, and liquid hourly space velocity to produce olefins and steam from a methanol feedstock; whereas the present invention relates to the process of contacting a methanol feedstock under oxygenate reaction conditions of elevated temperature and pressure and in the presence of a steamed or thermally treated catalyst of improved stability yet similar activity as the untreated catalyst to yield a predominantly gasoline range liquid hydrocarbon product.
There are references which disclose the use of mildly steamed zeolite catalysts in methanol-to-gasoline (MTG) conversion reactions.
U.S. Pat. No. 4,429,176 (Chester et al) incorporated herein by reference, discloses the use of a mildly presteamed catalyst in a methanol-to-gasoline (MTG) process (Column 8, line 46). The pretreated catalyst has increased stability over the fresh catalyst.
U.S. Pat. No. 4,522,929 (Chester et al) incorporated herein by reference, discloses the use of a mildly presteamed catalyst in a methanol-to-gasoline (MTG) process (column 8, line 43). The pretreated catalyst has increased stability over the fresh catalyst.
U.S. patent application Ser. No. 685,194, allowed, incorporated herein by reference, discloses the use of a mildly presteamed catalyst in a methanol-to-gasoline (MTG) process. The pretreated catalyst retains the activity of the fresh catalyst but has improved aging characteristics.